1. Field of the Invention
The invention generally relates to a sensing circuit and a sensing method thereof, and more particularly, to a capacitance sensing circuit and a capacitance sensing method thereof.
2. Description of Related Art
In this information era, reliance on electronic products is increasing day by day. The electronic products including notebook computers, mobile phones, personal digital assistants (PDAs), digital walkmans, and so on are indispensable in our daily lives. Each of the aforesaid electronic products has an input interface for a user to input his or her command, such that an internal system of each of the electronic product spontaneously runs the command. At this current stage, the most common input interface includes a keyboard and a mouse.
From the user's aspect, it is sometimes rather inconvenient to use the conventional input interface including the keyboard and the mouse. Manufacturers aiming to resolve said issue thus start to equip the electronic products with touch input interfaces, e.g. touch pads or touch panels, so as to replace the conditional keyboards and mice. At present, the users' commands are frequently given to the electronic products by physical contact or sensing relationship between users' fingers or styluses and the touch input interfaces. For instance, a capacitive touch input interface characterized by a multi-touch sensing function is more user-friendly than the conventional input interface and thus gradually becomes more and more popular.
However, given that the capacitive touch input interface is applied to a one-end sensing circuit, capacitance of a capacitor under test is required to be measured and stored as a base line capacitance before touch sensing. The base line capacitance is subtracted from the capacitance under test which is measured by the one-end sensing circuit, and thereby the capacitance variations of the capacitor under test can be obtained. Meanwhile, a reference capacitance of the capacitor under test measured by the one-end sensing circuit has a fixed value so that external noises cannot be effectively reduced and accordingly the noise-to-signal ratio (NSR) of the one-end sensing circuit cannot be effectively enhanced.